THE EVIDENCE OF THE SKELETON I21 
primitive cartilaginous cranium is always composed of the following 
parts :— 
1. A pair of cartilaginous plates on each side of the cephalic: 
section of the notochord known as the parachordals (pa.ch., Fig. 49 ; 
w., Fig. 48). These plates, together with the notochord (ch.) enclosed 
between them, form a floor for the hind and mid-brain. 
ch 
Fic. 48.—Empryo Pic, Two-rHirnps oF AN Fic. 49.—Hreap or Emsryo Dog-risH 
INCH LONG (from PaRKER), ELEMENTS (from ParKER), Basau VIEW OF CRANIUM 
oF SKULL SEEN FROM BELOW. FROM ABOVE. 
ch., notochord; iv., parachordals; au., ol., olfactory sacs; au., auditory capsule; 
auditory capsule; py., pituitary body; ¢r., py., pituitary body; pa.ch., parachordal 
trabecula; ctr., trabecular cornu; pn., cartilage; ¢7., trabecula; inf., infundi- 
pre-nasal cartilage ; ppg., palato-pterygoid bulum ; pi.s., pituitary space; ¢., eye. 
tract; mn., mandibular arch; th.h., first 
branchial arch; VII.-XTT., cranialnerves. 
2. A pair ot bars forming the floor for the fore-brain, known as 
the trabecule (ér). These bars are continued forward from the para- 
chordals. They meet posteriorly and embrace the front end of the 
notochord, and after separating for some distance bend in again in 
such a way as to enclose a space—the pituitary space (pt.s.). In 
